Traumatic brain injury 9TBI) has an incidence of nearly 2,000,000 cases per year, and is the leading cause of disability and death in children and young adults (peak incidence in 15 to 24 year olds) in the United States. Following mild head injury patients may suffer from a multitude of cognitive deficits including decreased speed in information processing, poor attention, concentration, and memory, and impaired logical reasoning skill, as well as more focal deficits including impairment of language or constructional abilities. A variety of other symptoms including headache, dizziness, nausea, neurasthenia, hyperesthesia, and emotional liability are commonly perceived. Head injury has been associated with short-term increased b-amyloid protein deposition and long-term neurotic plaques characteristic of Alzheimer's Disease. Epidemiological studies have observed a statistically-significant relationship between TBI and the subsequent onset of AD. Indeed, there is growing evidence that head injury, even mild in nature, may have greater consequences than previously assumed. The investigators hypothesize that mild/moderate TBI can cause neuronal cell death (reflected primarily by gray matter volume lose) and that this is the primary factor in induction and progression of neurocognitive disability in head injured patients. The central hypothesis is to test this hypothesis that the investigators have developed and validated computerized quantitative methods based upon magnetic resonance (MR) imaging (MRI) to measure the effect of TBI on brain substance. The investigators have also devised and implemented a proton (+H) magnetic resonance spectroscopy (MRS) technique to quantitative the neuronal concentration of the entire brain based upon the measurement of N-acetylaspartate (WBNAA) which is considered to be a marker of neuronal integrity. This proposal will correlate these quantitative MR measures with clinical measures of disability and neurocognitive tests. The overarching goal is to utilize MRI and 'H MRS to detect and quantify the effects TBI in a well-characterized cohort of mild/moderate head injured patients over a duration of 5 years. The results from this research will provide new and important information regarding the full extent of TBI, aid in categorizing these patients, and serve as an arbiter to assess proposed treatment strategies.